When a battery is charged by a charger, the battery may be charged rapidly with a large current using a constant current charge mode. In this case, however, the battery (especially, a lithium-ion battery) may be overcharged, so that the lifespan of the battery may be shortened and in a worst case scenario, the battery may catch fire.
Accordingly, in order to protect the battery, if the voltage increases close to the full charge state, the battery is charged with a prescribed constant voltage such that the charge current is naturally reduced. This charge mode is called a constant voltage charge mode.
In the case of a lithium-ion battery, if the battery voltage reaches, for example, 4.2 V, the charge mode is switched from the constant current charge mode (CCCM) to the constant voltage charge mode (CVCM). However, a rapid and/or large change in the charge current may adversely affect the battery, so it is desirable that the battery voltage be regulated naturally to 4.2 V while the charge current is kept constant.
Conventionally, a programmable resistor or switch is used to switch the charge mode from constant current charge mode to constant voltage charge mode.
However, the rapid transition of the charge mode using a programmable resistor or switch may lead to a rapid change in the charge current, which may shorten the lifespan of the battery.
Accordingly, a technique is known which uses a diode as a charge mode transition element in order to suppress the rapid transition of the charge mode. In this case, however, the use of the diode may increase the occupying area of the charging circuit as well as the manufacturing cost thereof, and a bias current may be needed.